1. Field of the Invention
The present invention relates generally to an automatic transmission for an automotive vehicle, and, more particularly, to a diagnostic system for watching on the sound operation of a kickdown switch provided in the automotive vehicle for controlling an automatic transmission incorporated therein so as to prohibit the transmission from operating at at least the highest speed stage when it detects a full depression of the accelerator pedal.
2. Description of the Prior Art
In the automotive vehicle equipped with an automatic transmission it is well known to incorporate a kickdown system in the transmission so that the transmission is prohibited from operating at at least the highest speed stage when the accelerator pedal is deeply depressed by the driver so that the transmission is shifted down from the highest speed stage to the next or further lower speed stage when it is operating at the highest speed stage or to prohibit the transmission from shifting up to the highest speed stage as long as the accelerator pedal is fully depressed by the driver for generating more power in the engine. In the conventional oil hydraulic control system in the automatic transmission the kickdown system generally comprises an oil hydraulic circuit which is activated by a full depression of the accelerator pedal to supply a line pressure in the system to a control port of an oil hydraulic change over valve which establishes the highest speed stage. In such a conventional mechanical and oil hydraulic kickdown system it is generally improbable that the system gets out of order throughout the normal life of operation of the vehicle.
However, in the modern automotive vehicle equipped with an electrically controlled automatic transmission, the kickdown system includes a kickdown switch of the type of an electrical limit switch which detects a full depression of the accelerator pedal by the driver and provides the electronic computer with information regarding the full depression of the accelerator pedal. However, such limit switch type electric switches available at present are generally more delicate and vulnerable to malfunction as compared with the strong and durable mechanical and hydraulic control system.
In fact, we have come to notice that the electric kickdown switches forming a part of the electrically controlled automatic transmissions in the modern automotive vehicles sometimes get out of order so as not to close when they are to close by a full depression of the accelerator pedal or to remain as closed regardless of the depression of the accelerator pedal. If the kickdown switch has broken so as constantly to indicate the full depression of the accelerator pedal the transmission will remain as being prohibited from shifting up to the highest speed stage. Such a malfunction will generally be noticed by every driver. On the other hand, however, if the kickdown switch has broken not to detect any full depression of the accelerator pedal so as thereby to nullify the kickdown performance of the automatic transmission, the defect is often overlooked without being noticed, particularly when the driver is not skilled in the driving or not much sensitive to the driving performance of the vehicle. This happens more often when the transmission provides an overdrive stage as its highest speed stage.